Segmented couplings for pipes are well known in the art, and comprise two or more coupling segments each having a recess for the reception of a sealing gasket adapted to extend over the adjacent ends of a pair of pipes, and which is to be compressed by the coupling segments into sealing relation with the external peripheries of the respective pipes.
Each coupling segment has radially inwardly extending keys at its opposite axial sides, the keys being for reception in grooves in the respective pipe ends to perform the required mechanical interconnection between the pipes.
The coupling segments are drawn towards each other by traction bolts which extend through radially outwardly extending bolting pads at the respective opposite ends of the coupling segments. In this manner, the end faces of the coupling segments are drawn towards each other for them to clamp onto each other in the case of a "flexible" coupling, or, for the coupling segments to clamp directly onto the pipe exterior in the case of a "rigid" coupling. It is explained that a "flexible" coupling is one which will permit relative movement of the pipes to limited extents and the angling of the axis of one of the pipes relative to the other, whereas a "rigid" coupling is one which will immobilize the pipes against any such movements.
Typical of such couplings are the ones shown in Nakamura U.S. Pat. No. 3,664,691, in Piatek U.S. Pat. No. 3,054,629, and Blakely U.S. Pat. No. 3,695,638, each of which teach coupling segments having end faces that extend parallel to the X-Z plane of the coupling, i.e., parallel to the longitudinal axis of the respective pipes.
Such couplings readily can be provided in "flexible" form. However, unless the end faces of the coupling segments ultimately remain spaced from each other, no guarantee can be made that the coupling is a truly "rigid" coupling, in that the pipes themselves will vary in external diameter within the permitted range of manufacturing tolerances of such pipes. If the end faces of the coupling segments remain spaced from each other, then, there is the necessity of providing extrusion shields spanning the gaps between the mutually presented end faces in order to prevent gasket extrusion under high internal pressures.
More recent developments in "rigid" couplings are shown in Rung et al. U.S. Pat. No. 4,611,839, which teaches a segmented coupling that is truly "rigid" despite variations in the pipe diameters within the accepted range of manufacturing tolerance of the pipes. This is accomplished by arranging for the end faces of the coupling segments to be inclined at angles relative to the X-Z plane of the coupling, the inclination of the end faces either being in the same direction relative to the X-Z plane of the coupling as shown in FIG. 9 of the patent, or, being in opposite directions relative to the X-Z plane of the coupling as shown in FIG. 12 of this patent.
In the event that the coupling faces are inclined in the same direction, while the coupling segments maY be identical with each other, they are not symmetrical, i.e., they can onlY be assembled one to the other in one position of the coupling segments.
However, if the end faces of the coupling segments are oppositely inclined relative to each other, then, coupling segments are provided which not only are identical one with the other, but which are also truly symmetrical one with the other, i.e., one of the coupling segments can be assembled to the other in a first position, and equally well can be rotated 180 degrees about the Y axis of the coupling and also correctly assembled to the other coupling segment.
Thus, in coupling segments of the type in which the end faces of the coupling segments extend parallel to the X-Z plane of the coupling for the coupling segments to be both identical and symmetrical, and in the FIG. 12 embodiment of the Rung et al. patent in which the end faces of the coupling segments are inclined relative to the X-Z plane of the coupling, but in opposite directions, there exists the possibility of assembling one of the coupling segments to the other either in the first position, or in a position rotated 180 degrees about the Y axis of the coupling.
This poses no particular problems in the case that both pipes are of the same external diameter. It can, however, result in disastrous consequences in the event that the external diameter of one of the pipes is different from the external diameter of the other pipe by an amount greater than the permissible range of manufacturing tolerances of either one of the pipes.
Young, U.S. Pat. No. 3,680,894 is specifically directed to a segmented coupling for use with pipes of external diameters different from each other, the coupling segments of this patent also having end faces which extend parallel to the X-Z plane of the coupling. Young's coupling is, however, intended for use on pipes of different internal diameters, and thus of appreciably different external diameters, in view of which the possibility of mis-assembly of the coupling segments onto the pipes with one of the coupling segments in a reversed condition will be readily apparent to the workman assembling the coupling. In fact, the coupling will not assemble, in that the internal diameter of the coupling segment intended for the smaller diameter pipe will not pass over the larger external diameter of the larger pipe.
If, however, a Young-type coupling is employed for joining two pipes of only slightly different external diameters, as in the case of joining cast iron pipe to drawn steel pipe of the same nominal size, then, a Young coupling could be inadvertently misassembled onto the pipes.
Through inadvertence, it is quite possible for a workman to assemble one of the coupling segments with its correct internal diameters presented to the pipes, and then to present the other coupling segment to the pipes in a reversed condition with its smaller internal diameter intended for presentation to the smaller external diameter of the steel pipe actually presented to the larger external diameter of the cast iron pipe, and, with the larger internal diameter of the coupling segment intended for the cast iron pipe presented to the smaller external diameter of the steel pipe. This can readily happen in that the difference in external diameter of the respective pipes is quite small. Further, during the assembly of the coupling the keys of the respective coupling segments are at that time concealed within the grooves of the respective pipes, and can not be visually observed, this removing a possible indication to the workman that the coupling has been incorrectly assembled.
If now the workman completes the assembly of the joint with the coupling segments improperly positioned, this may result in a defective joint, in that the sealing gasket will be improperly compressed into engagement with the external peripheries of the pipes. This can be of disastrous consequences in the event that the pipes are intended for the handling of high internal pressure, or, for the handling of noxious gases or highly flammable liquids.